Flat panel displays have become increasingly important in appliances requiring lightweight portable screens. Currently, such screens use electroluminescent or liquid crystal technology. A promising technology is the use of a matrix-addressable array of cold cathode emission devices to excite phosphor on a screen.
Spindt, et. al. discuss field emission cathode structures in U.S. Pat. Nos. 3,665,241, and 3,755,704, and 3,812,559, and 5,064,396. To produce the desired field emission, a potential source is provided with its positive terminal connected to the gate, or grid, and its negative terminal connected to the emitter electrode (cathode conductor substrate). The potential source may be made variable for the purpose of controlling the electron emission current. Upon application of a potential between the electrodes, an electric field is established between the emitter tips and the low potential anode grid, thus causing electrons to be emitted from the cathode tips through the holes in the grid electrode, and then onto a phosphor coated anode screen.
An array of points in registry with holes in low potential anode grids are adaptable to the production of cathodes subdivided into areas containing one or more tips from which areas emissions can be drawn separately by the application of the appropriate potentials thereto.
In U.S. Pat. No. 3,970,887, entitled, "Micro-structure Field Emission Electron Source," Smith et al describe a method of electrically isolating emission sites by appropriately doping the semiconductor substrate to provide opposite conductivity type regions at the field emission sites.
The field emission sites of the present invention are physically isolated by a dielectric layer which has a high resistance. The dielectric layer is deposited in a trough or trench created in the substrate. A polysilicon layer or other suitable conductive material, such as titanium salicide, is deposited on top of the dielectric layer, thereby providing good electrical signal propagation down the row (or column) of emitters.
One advantage of the present invention is an increase in process and design flexibility which results from the fact that the cathode material is decoupled from the substrate by the presence of the insulator. Another advantage is the greater range of materials which can be used for both the substrate and the emitters.
A further advantage of the trench isolated accessibility of the emitter tips according to the present invention, is the elimination of the need for costly implants. Leakage is also reduced.
A still further advantage is that the conductive material used to form the trench accesses can be different from the material used to form the cathode emitters, thereby increasing the speed and efficiency of the display. The highly conductive material deposited in the trenches can be selected from a group of materials having good electrical signal propagation abilities, and the cathode material can be selected for electron emission capabilities.